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Unformatted text preview: Eleventh International Conference, The Jack-Up Platform - September 11th and 12th 2007 London Mat-Supported Jack-Up Foundation On Soft Clay Overturning Storm Stability, W.P. Stewart Mat-Supported Jack-Up Foundation On Soft Clay Overturning Storm Stability Foundation On Soft Clay Overturning Storm Stability W.P. Stewart, with support from various companies and consultants. Stewart Technology Associates Abstract The Maleo Producer is a converted Bethlehem JU 250 (1970s design) mat-supported jack-up that is now operating as a gas production platform in Indonesia. The platform is owned and operated by Global Production Solutions (GPS) and produces gas for Santos. Extensive investigations into the sea bed soils around the in-place structure and analyses of its foundation static and dynamic strength characteristics were undertaken in the first half of 2007. This paper provides an overview of the calculation methodology of the structures overturning resistance site to storm loading on the soft clay at the site. The soil strength characteristics and method of computing bearing capacity and overturning resistance of the mat foundation are described. The methods adopted were accepted by ABS for class approval of the structure as an offshore installation. Shallow Foundation Capacity Mat supported jack-up foundations on soft clays may be assessed using the shallow foundation capacity equations given, for example, in API RP2A. However, while these equations deal with bearing capacity for shallow mats and strip footings, the designer is left with uncertainties as to how to treat mats with large cut outs and fingers around the mat slot. The uncertainties become greater when the overturning resistance is considered. Part of the dilemma is to assess when a mat with cut outs should be treated as an equivalent area mat and when it should be treated as a series of strip footings. In most soft clay offshore sites the difficulties of assessing mat foundation capacities are further compounded by the increasing strength of the soil with depth. In very soft soils, on level sea beds, mat rigs will penetrate into the sea bed until a depth is reached where the soil bearing capacity is just sufficient to support the weight of the structure (less it buoyancy) if the mat is kept level and is caused to penetrate slowly. The consequence of the structure not penetrating evenly, but rocking during penetration may result in deeper final penetration of the mat. The effects of uneven penetration causing the structure to tilt back and forth and the bearing pressures to increase and decrease from one side of the mat to the other are difficult to assess. Such effects are considered to have played a significant role in the installation of the Maleo producer....
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This note was uploaded on 04/19/2010 for the course CIVL 306455301 taught by Professor Mudiliu during the Three '09 term at University of Sydney.
- Three '09